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JAMA Network Open: Seropositive Prevalence of Antibodies Against SARS-CoV-2 in Wuhan, China

Large-scale population-based serological studies can help us better understand the true scale of COVID-19 and the immune characteristics of patients after infection. Recently, JAMA Network Open, a subsidiary of the Journal of the American Medical Association, published the results of a survey on the seropositive rate of COVID-19 antibodies in the Wuhan, China. The study was carried out by a team from Tongji Hospital of Huazhong University of Science and Technology.

This cross-sectional study was conducted at Tongji Hospital from March 27 to May 26, 2020, and included 3,040 adults aged 18 and over, 49.3% of whom were males, with a median age of 36 years (interquartile range 30 to 45 years). The research team performed serum tests for their IgM and IgG antibodies to SARS-CoV-2, and nucleic acid tests by PCR for SARS-CoV-2.

The results showed that the overall serum antibody positive rate was 3.9%. The positivity rate for IgM antibodies only was 0.0%, that for both IgM and IgG antibodies was 0.7%, and that for IgG antibodies only was 3.2%. Among the 1360 individuals with positive antibodies, most (80.9%) were IgG positive only. Only a few individuals (0.04%, 15 cases/35040 cases) detected the SARS-CoV-2 viral nucleic acid sequence in their bodies and turned negative during the quarantine period. No positive nucleic acid test was found in their close contacts. This means that most of the infections of subjects who have tested positive for serology are those that have occurred before, rather than newly infected people.

From the distribution of population characteristics, the seroprevalence rate in urban areas is higher than that in suburban and rural areas (4.4% vs 2.9%), which is consistent with the geographical distribution of confirmed cases. The seroprevalence rate of women is higher than that of men (4.4% vs 3.3%), which is consistent with the higher diagnosis rate of women previously reported. With age, the seroprevalence rate is higher, and the seroprevalence rate for people 60 years and older is 9.2%. The research team pointed out that the proportion of comorbidities in the elderly may be higher, which may increase the risk of COVID-19 infection and increase the severity of the disease

The research team also pointed out that although the overall sample size is large, some factors also have an impact on the results. For example, the participants did not include minors, and there were very few people over 60, which limited the estimation of the seroprevalence of the elderly and children; at the same time, most participants were from urban areas with higher infection rates. It may affect the accuracy of the seroprevalence rate. In addition, the specific antibodies against SARS-CoV-2 might wane over time in some convalescent COVID-19 individuals, asymptomatic cases who had low levels of antibodies might be more likely to become negative in population-based studies.

 

Reference:

  1. Liu, A., et al.(2020). Seropositive Prevalence of Antibodies Against SARS-CoV-2 in Wuhan, China. JAMA Network Open, 3(10), (2020) e2025717-e2025717.

 

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